1. Field of Invention
The present invention relates to an attachment apparatus for a heater for attaching the heater, which is configured in an almost circular shape in its side view and cut at a circumferential portion thereof to form opposite circumferential end portions, to the external peripheral portion of a heated member of a cylindrical or column shape. In particular, the invention relates to an attachment apparatus for a heater suitable to be provided at the external peripheral portion of a heat cylinder of an injection molding machine for metal.
2. Related Art
Metal molded items made of magnesium alloy, aluminum alloy etc., for example, are also formed by the injection molding. The injection molding machine for metal used for such injection molding is configured, as is well known, by a heat cylinder, a screw provided within an inner hole of the heat cylinder so as to be able to be driven in the axial direction and the rotational direction, and a screw driving device for driving the screw etc. An injection nozzle is provided at the front portion of the heat cylinder. Each of the heat cylinder and the injection nozzle is provided at its outer peripheral portion with a plurality of electric heaters, that is, heaters which are adapted to control the temperature independently. Thus, at the time of measuring an amount, as is well known, the metal material supplied to the heat cylinder is melted by the heat mainly supplied from the heater, then accumulated at the front portion of the heat cylinder and subject to the amount measurement.
As shown in (a) of FIG. 2, such a heater 30 is configured in an almost circular shape in its side view by a heat portion 33 formed by the combination of an insulator 31 made of ceramic, mica etc. and a nichrome wire 32, and a heater outer cover 34 for protecting the heat portion 33. The heater is cut at a portion to have abutment portions 35, 35xe2x80x2. As also shown in (b) of FIG. 2, the attachment apparatus for the heater 30 is formed by a pair of attachment metal members 36, 36xe2x80x2, a pair of rod-shaped members 37, 37xe2x80x2 and a bolt 38 etc. The pair of attachment metal members 36, 36xe2x80x2 are bent in ring shapes and fixed in the vicinity of the abutment portions 35, 35xe2x80x2 of the heater 30 by the welding, respectively. The rod-shaped member 37xe2x80x2 is provided with a through hole through which the shaft portion of the bolt 38 is passed and the other rod-shaped member 37 is provided with female screw or internal threads to be engaged with the bolt 38. The heater 30 is attached to the external peripheral portion of a heated member of a cylindrical or column shape, for example, a heat cylinder 40 in the following manner by using the aforesaid attachment metal members 36, 36xe2x80x2. That is, the heater 30 is attached to the external peripheral portion of the heat cylinder 40, and then the pair of the rod-shaped members 37, 37xe2x80x2 are inserted into the ring-shaped bent portions of the attachment metal members 36, 36xe2x80x2, respectively. Then, the shaft portion of the bolt 38 is inserted into the through hole of the other rod-shaped member 37xe2x80x2 and the bolt 38 is screwed into the threads of the one rod-shaped member 37. Thus, the abutment portions 35, 35xe2x80x2 are attracted to each other and so the heater 30 is adhesively attached to the external peripheral portion of the heat cylinder 40.
Although not shown in the drawings, the heater is also attached to the heat cylinder by using a marketed commodity called as a catch clip or a snap fastener in place of the aforesaid attachment apparatus.
Although the heater 30 can be attached to the heat cylinder 40 by using each of the aforesaid attachment apparatus and the marketed commodity called as the catch clip or the snap fastener, there arises many problems. For example, there may arise a case that the heater 30 can not be removed in order to replace it for a new one. That is, in the case of heating the heat cylinder 40 of the injection molding machine for metal to 550xc2x0 C. by using the heater 30 which normal usage temperature is set at 550xc2x0 C., the temperature of the heater 30 itself may not be limited to 550xc2x0 C. and the temperature of the heater outer cover 34 may increase to a temperature higher about 200 to 400xc2x0 C. than 550xc2x0 C. which is the heating temperature of the heat cylinder 40. In particular, when the heater outer cover 34 is heated in a state that heat reserving material is wound around the outside of the heater outer cover in order to prevent the heat radiation, the temperature of the heater outer cover 34 further increases. Thus, it is experienced in the heat cylinder of the injection molding machine for metal that since the bolt is heated to such a high temperature, the bolt 38 is burnt, whereby the heater 30 can not be removed for replacing it for a new one unless the attachment apparatus of the heater 30 is broken. Although it is considered that such a burning phenomenon can be prevented when burning prevention material such as high-temperature heat-resistant grease etc. is coated on the bolt 38, it is experienced that the burning prevention material does not attain any effect in the heat cylinder of the injection molding machine for metal. Further, the grease itself may be burnt and hardened depending on an amount of the grease coated to thereby obstruct the removal of the bolt 38.
Furthermore, since the degree of adhesion of the heat portion 33 of the heater 30 to the heat cylinder 40 reduces, there arises various problems. That is, the heater outer cover 34 is generally formed by stainless steel and the heater outer cover 34 is pulled by the bolt 38 of the attachment apparatus, so that the heat portion 33 is adhered to the heat cylinder 40. Such a pulling force can be adjusted depending on the fastening force of the bolt 38. As for the heat cylinder 40 of the injection molding machine for metal, the bolt is fastened so that a high tension of about 70 to 100N is applied to the heater outer cover. When the heater 33 is made conductive in a state where such a high tension acts on the heater outer cover, the heater outer cover 34 increases in its temperature and expands earlier than the heat cylinder since the heat capacity of the heater outer cover 34 is smaller than that of the heat cylinder 40. Although the heat cylinder 40 also increases in its temperature with the lapse of the time, since the heat cylinder 40 is larger in its volume than the heater outer cover 34, the heat cylinder is larger in its amount of the expansion than the heater outer cover and hence the heater outer cover 34 further expands. In other words, the heater outer cover 34 expands due to the creep phenomenon caused by the time difference of the thermal expansion between the heat cylinder and the heater outer cover, so that the setting fastening force can not be maintained. As a result, the heat portion reduces in its degree of the adhesion to the heat cylinder and there appears gaps partially between the heat cylinder and the heater outer cover. When the degree of the adhesion reduces in this manner, the heat transmission coefficient between the heat cylinder and the heat portion reduces. Further, when there appears gaps partially between the heat cylinder and the heat portion, the heat transmission efficiency therebetween varies or becomes uneven partially, which results in the cause of the xe2x80x9cbending phenomenonxe2x80x9d of the heat cylinder 40 and adversely affects the heat cylinder 40 due to the thermal stress. Furthermore, an amount of heat transmitted from the heat portion 33 to the heat cylinder 40 reduces due to the gaps, whereby the temperature of the heat portion 33 increases partially to an excessive value. Thus, the life time of the nichrome wire 32 becomes shorter since the oxidization of the nichrome wire 32 proceeds. Further, the nichrome wire 32 melts due to the excessive temperature, which results in the breaking of the wire.
The aforesaid phenomenon also results in the reduction of the producibility. To be more concrete, although the heater 30 should be exchanged in a short time as possible in view of the producibility, the temperature of the heat cylinder 40 reaches about 600xc2x0 C. during the operation and so it is hard to operate the bolt 38. Further, as described above, since the bolt 38 is burnt, it is quite difficult to exchange the heater. As a result, the exchange procedure of the heater can not be performed until the temperature of the heat cylinder 40 decreases, which results in a cause of reduction of the working ratio.
In this respect, the catch clip or the snap fastener can be operated relatively easily and so the attachment and the removal of the heater 3 can be easily performed relatively, but these commodities are complicated in the construction and the component parts thereof are expensive. Further, since all the constituent parts of these commodities are integrated by the welding etc., there is a draw back that the these commodities can not be used repeatedly since it is impossible to exchange only broken or damaged parts. As a countermeasure, it is considered that the apparatus is fabricated by heat-resistant material such as Inconel 718 to improve the efficiency of the apparatus such as durability etc. However, in this case, the cost of the apparatus further increases. Thus, when the heater 30 is broken, it is uneconomical since the expensive constituent parts as well as the heater 30 must be disposed simultaneously.
Accordingly, an object of the invention is to provide an attachment apparatus for a heater which is formed by the aforesaid conventional bolt etc. or which eliminates the aforesaid problems and drawbacks etc. of the catch clip or the snap fastener. To be concrete, an object of the invention is to provide an attachment apparatus for a heater which can easily attach and remove the heater, maintain high degree of the adhesion between the heater and a heated member, and be low in cost.
In order to attain the aforesaid object, the invention is arranged in a manner that in an attachment apparatus for a heater for attaching the heater, which is configured in an almost circular shape in its side view and cut at a circumferential portion thereof to form opposite circumferential end portions, to an external peripheral portion of a heated member of a cylindrical or column shape, the attachment apparatus includes a pair of stop metal members fixed near the circumferential end portions of the heater and a spring, wherein both end portions of the spring are engaged with the stop metal members in a state being pulled by the stop metal members with a predetermined tension, respectively, whereby the opposite circumferential end portions of the heater are attracted to each other and so the heater is elastically adhered to the external peripheral portion of the heated member.
In the present invention, the spring is separated from the heater by a predetermined length outward to a radial direction.
In the present invention, a plurality of the springs are provided in parallel.
In the present invention, the heated member is a heat cylinder of an injection molding machine for metal.